鄂尔多斯盆地大牛地气田二叠系山西组砂体叠置模式及油气开发意义

Sandbody superimposition patterns and oil and gas exploration significance of Permian Shanxi Formation in Daniudi gas field,Ordos Basin

河流相砂体储层构型对致密砂岩中相对优质储层的分布规律和天然气开发具有重要意义。通过野外地质剖面和钻井岩心观察,结合测井、录井和岩心分析测试资料,对鄂尔多斯盆地大牛地气田大12井区二叠系山西组致密砂岩的砂体构型要素、叠置模式及油气开发意义进行了研究。研究结果表明:(1)鄂尔多斯盆地大牛地气田大12井区二叠系山西组发育六级复合辫流带和五级单一辫流带,其中单一辫流带包括河床(分流河道)和河漫共2个四级构型单元,河道内单个心滩沉积包含有三级增生体和落淤层;(2)辫状河三角洲平原五级单一辫流带中的四级泛滥平原沉积较辫状河河漫沉积更加发育,辫状河心滩沉积中落淤层欠发育;(3)山西组上部山2-2亚段辫状河单一辫流带内砂体呈“河道-心滩”连续沉积,泥质不发育,砂体叠置程度高(多呈复合式叠置)、连通性好,优质储层多;(4)山西组中下部山1段和山2-1亚段三角洲平原沉积中,西部河道连片性好,砂体以复合式和侧拼式叠置样式为主,连通性和生产效果均较好,东部砂体多为孤立式和侧接式,砂体钻遇率低,单井产量差。

The reservoir configuration of fluvial facies sand bodies is of great significance for the distribution of high-quality tight sandstone reservoirs in tight sandstone and natural gas development.Through field geological profiles and drilling cores observation,combined with logging and core analysis testing data,the sand body configuration elements,stacking patterns and oil and gas development significance of tight sandstones of Permian Shanxi Formation in Da 12 well area of Daniudi gas field in Ordos Basin were studied.The results show that:(1)The Permian Shanxi Formation in the study area developed six-level composite braided flow zones and five-level single braided flow zone,the single braided flow zone includes river bed(distributary channel)and river diffuse,the mid-channel bar contains three-level accretion bodies and siltation layers.(2)The four-level floodplain deposits in the five-level single braided flow zone of braided river delta plain are more developed than the river diffuse in the braided river,and the siltation layer in the mid-channel bar is less developed.(3)The sand bodies in the single braided flow zone of the braided river in Shan 2-2 sub-member of Shanxi Formation are continuously deposited in a pattern of“channel to mid-channel bar”,with undeveloped shale and high degree of sand body stacking(mostly in composite stacking),good connectivity,and many high-quality reservoirs.(4)In the delta plain de-posits of Shan 1 member and Shan 2-1 sub-member of Shanxi Formation,the river channels in the west have good connectivity,and the sand bodies are mainly composite and side-jointed superimposed,with good connec-tivity and production effects,while the sand bodies in the east are mainly of isolated and side-jointed styles,with low sand body drilling rate and low single well production.